A method and a CT unit are known, for example, from laid-open patent application DE 198 42 238 A2. This document discloses a recording method for a periodically moving object, in particular a patient's beating heart, having a moving phase and a rest phase via a CT unit having a gantry, rotating spirally around the examination object, with a focus and a multirow detector, the feed rate of the patient couch and the rotational speed of the gantry being tuned to one another for a complete pass or scan in such a way that it is possible to collect sufficient image information for the best possible reconstruction during the rest phase of the periodically moving object. The movement and rest phases can be determined by a connected ECG. No provision is made to change the feed rate during the scan.
A disadvantage with this is a need for a relatively low feed rate that thereby also necessitates accepting a high dose commitment during recording.
Reference is also made to patent U.S. Pat. No. 5,046,003, which describes a method of sequential scanning in which individual image planes are scanned by a single-row detector by moving at the lowest possible feed rate in the local region of these image planes, whereas the feed rate is raised with increasing distance from the nearest image plane. This results in a virtually sinusoidal characteristic of the feed rate over the entire scanning path independently of the movement situation in the scanned area. It appears to be a problem here that the feed rate changing cyclically and in short intervals transfers onto the patient as a whole an uncontrolled movement that leads to fuzziness in the CT recordings.
Also generally known—for example from “Bildgebende Systeme der medizinischen Diagnostik” [“Imaging Systems in Medical Diagnostics”], ISBN 89578-002-2, or “Computer-Tomographie” [“Computer tomography”], ISBN 3-89578-082-0, —on the other hand are the most multifarious CT recording methods, including special reconstruction methods of resting objects, a constant feed rate being used in each case for a complete pass of a scan.
A disadvantage of such methods resides in the poor recording quality as a result of the movement fuzziness in the area of the respectively moving part of the object to be recorded, for example the heart in the case of a patient.
If the aim now is to carry out a CT scan of a patient's lung, the movement of the beating heart leads to instances of movement fuzziness in the area of fine vessels. This movement fuzziness also produces unsatisfactory recording results when differential images are produced from native and contrastive measurements in order to determine the lung perfusion. The two measurements lie apart by approximately 10 seconds, and so they can be carried out with fast CT units during a breath-holding cycle. Nevertheless, the heart movement leads to an interim change in position of the lung and to a displacement between native and contrastive image. Were the recording to be carried out, alternatively, in accordance with the method of a cardio CT, on the one hand the recording period would be too long such that a breath-holding cycle would be insufficient for the two recordings, and on the other hand the applied dose would be too high for the patient.